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B C Wang

Publications and source records attributed to B C Wang.

At least 19 recordsLinked to original sources
PubMed1998

The structure of glutamine-binding protein complexed with glutamine at 1.94 A resolution: comparisons with other amino acid binding proteins.

The crystal structure of the glutamine-binding protein (GlnBP) complexed with its ligand (Gln) was determined and refined to 1.94 A resolution. This ellipsoidal protein has two globular domains and is approximately 52 Ax40 Ax35 A in size. The glutamine ligand is located in the cleft between the two domains and stablized by hydrogen bondings and ionic interactions with Asp10, Gly68, Thr70, Ala67, Asp157, Arg75, Lys115, Gly119 and His156. The aliphatic portion of the glutamine ligand is sandwiched in a hydrophobic pocket formed between Phe13 and Phe50 and has 21 van der Waals contacts with GlnBP. Lys115 and His156, that are unique to GlnBP among amino acid binding proteins, apparently contribute to the ligand binding specificity of GlnBP. Asp10 is within 3 A of Lys115. These two residues are over 10 A apart in the ligand-free form of the GlnBP. In addition, GlnBP-Gln exhibits a large-scale movement of the two hinges connecting the two globular domains upon ligand binding. The most significant changes are 41.1 degrees in the phi angle of Gly89 and 34.3 degrees in the psi angle of Glu181 from the first and the second hinge of the protein, respectively. Besides the original six hydrogen bonds, three extra hydrogen bonds can be observed between the two hinge strands upon ligand binding. A hydrogen bond network connects the large domain to the second hinge and a second hydrogen bond network coalesces the small domain to the same strand, both via interaction with the glutamine ligand. Although the two strands of the hinge connecting the domains do not directly participate in the ligand binding, Gln183 and Tyr185 from the second hinge may be involved in the cascade of the conformational change that is induced by ligand binding.

Amino Acid Sequence↗
PubMed1998

Structural modeling of the pro-ocytocin-neurophysin precursor.

The hormonal precursor pro-ocytocin-neurophysin is activated by selective cleavage at Arg2-Ala13, producing mature ocytocin and neurophysin. To understand the cleavage mechanism better, and in particular the recognition of the cleavage site, it is necessary to characterize the three-dimensional structure of the precursor molecule. Here we combine a variety of experimental data with molecular modeling and dynamics calculations to derive possible precursor conformations. In the models obtained, the N-terminus of the precursor, corresponding to the ocytocin segment, is hydrogen bonded in a pocket of the neurophysin moiety in a similar manner to a crystallographically obtained non-covalent complex between the two molecules. The calculations suggest that although the ocytocin segment is relatively flexible, it adopts a stable, broad loop structure in the vicinity of the cleavage region, which may constitute the structural element recognized by the cleaving enzyme. The calculations also suggest a possible widening of the distance between the two neurophysin domains in the precursor relative to that in the non-covalent neurophysin-ocytocin complex.

Amino Acid Sequence↗
PubMed1997

In vitro and in vivo mechanical evaluations of plasma-sprayed hydroxyapatite coatings on titanium implants: the effect of coating characteristics.

This study was undertaken to evaluate the effect of coating characteristics on the mechanical strengths of the plasma-sprayed HA-coated Ti-6Al-4V implant system both in vitro and in vivo. Two types of HA coatings (HACs) with quite different microstructures, concentrations of impurity-phases, and indices-of-crystallinity were used. In vitro testings were done by measuring the bonding-strength at the Ti-6Al-4V-HAC interface, with HACs that had and had not been immersed in a pH-buffered, serum-added simulated body fluid (SBF). The shear-strength at the HAC-bone interface was investigated in a canine transcortical femoral model after 12 and 24 weeks of implantation. The results showed a bonding degradation of approximately 32% or higher of the original strength after 4 weeks of immersion in SBF, and this predominantly depended on the constructed microstructure of the HACs. After the push-out measurements, it was demonstrated that the HACs with higher bonding-strength in vitro would correspondingly result in significantly higher shear-strength at each implant period in vivo. Nevertheless, there were no substantial histological variations between the two types of HACs evaluated. The most important point elucidated in this study was that, among coating characteristics, the microstructure was the key factor in influencing the mechanical stability of the HACs both in vitro and in vivo. As a consequence, a denser HAC was needed to ensure mechanical stability at both interfaces.

Adhesiveness↗
PubMed1997

Intramedullary implant of plasma-sprayed hydroxyapatite coating: an interface study.

An intramedullary implant model in the canine femora was developed to evaluate the mechanical and histological responses between cancellous bone and plasma-sprayed hydroxyapatite coatings (HACs) on ti-6A1-4V implants, with 12- and 24-week follow-ups. HACs of different thicknesses were investigated. Results of the mechanical testings revealed that after 24 weeks of implantation, the mean shear strength (2.49 +/- 0.12 MPa) of the 50 microns HACs was significantly higher (p < 0.05) than that of the 200 microns HACs (1.44 +/- 0.19 MPa). However, using backscattered electron images (BEIs) throughout all the implant periods, no substantial histological variations in the extent of new bone apposition between the two HACs were observed. Occasionally, solution-mediated disintegration of the 50 microns HAC was found 24 weeks postimplantation. Histomorphometric studies from the BEIs demonstrated that for both HACs the percentage of the direct HAC-cancellous bone contact was approximately 50% at 12 weeks and 75% at 24 weeks. After the mechanical tests, the 200 microns HACs had fracture sites either inside the coating layers or at the HAC-titanium interfaces, which might explain why the mechanical performance of the 200 microns HACs was inferior to that of the 50 microns HACs even though both HACs had the same histological behaviors.

Alloys↗
PubMed1997

The first structure of an aldehyde dehydrogenase reveals novel interactions between NAD and the Rossmann fold.

The first structure of an aldehyde dehydrogenase (ALDH) is described at 2.6 A resolution. Each subunit of the dimeric enzyme contains an NAD-binding domain, a catalytic domain and a bridging domain. At the interface of these domains is a 15 A long funnel-shaped passage with a 6 x 12 A opening leading to a putative catalytic pocket. A new mode of NAD binding, which differs substantially from the classic beta-alpha-beta binding mode associated with the 'Rossmann fold', is observed which we term the beta-alpha,beta mode. Sequence comparisons of the class 3 ALDH with other ALDHs indicate a similar polypeptide fold, novel NAD-binding mode and catalytic site for this family. A mechanism for enzymatic specificity and activity is postulated.

Aldehyde Dehydrogenase↗
PubMed1996

The crystal structure of glutamine-binding protein from Escherichia coli.

The crystal structure of the glutamine-binding protein (GlnBP) from Escherichia coli in a ligand-free "open" conformational state has been determined by isomorphous replacement methods and refined to an R-value of 21.4% at 2.3 A resolution. There are two molecules in the asymmetric unit, related by pseudo 4-fold screw symmetry. The refined model consists of 3587 non-hydrogen atoms from 440 residues (two monomers), and 159 water molecules. The structure has root-mean-square deviations of 0.013 A from "ideal" bond lengths and 1.5 degrees from "ideal" bond angles. The GlnBP molecule has overall dimensions of approximately 60 A x 40 A x 35 A and is made up of two domains (termed large and small), which exhibit a similar supersecondary structure, linked by two antiparallel beta-strands. The small domain contains three alpha-helices and four parallel and one antiparallel beta-strands. The large domain is similar to the small domain but contains two additional alpha-helices and three more short antiparallel beta-strands. A comparison of the secondary structural motifs of GlnBP with those of other periplasmic binding proteins is discussed. A model of the "closed form" GlnBP-Gln complex has been proposed based on the crystal structures of the histidine-binding protein-His complex and "open form" GlnBP. This model has been successfully used as a search model in the crystal structure determination of the "closed form" GlnBP-Gln complex by molecular replacement methods. The model agrees remarkably well with the crystal structure of the Gln-GlnBP complex with root-mean-square deviation of 1.29 A. Our study shows that, at least in our case, it is possible to predict one conformational state of a periplasmic binding protein from another conformational state of the protein. The glutamine-binding pockets of the model and the crystal structure are compared and the modeling technique is described.

Amino Acid Sequence↗
PubMed1996

Crystal structure of the neurophysin-oxytocin complex.

The first crystal structure of the pituitary hormone oxytocin complexed with its carrier protein neurophysin has been determined and refined to 3.0 A resolution. The hormone-binding site is located at the end of a 3(10)-helix and involves residues from both domains of each monomer. Hormone residues Tyr 2, which is buried deep in the binding pocket, and Cys 1 have been confirmed as the key residues involved in neurophysin-hormone recognition. We have compared the bound oxytocin observed in the neurophysin-oxytocin complex, the X-ray structures of unbound oxytocin analogues and the NMR-derived structure for bound oxytocin. We find that while our structure is in agreement with the previous crystallographic findings, it differs from the NMR result with regard to how Tyr 2 of the hormone is recognized by neurophysin.

Amino Acid Sequence↗
PubMed1996

The evaluation of a new 7-day gonadotropin-releasing hormone agonist protocol in the controlled ovarian hyperstimulation for in vitro fertilization.

OBJECTIVE: Gonadotropin-releasing hormone agonist (GnRHa) was used in the controlled ovarian hyperstimulation (COH) for the in vitro fertilization program. However, the traditional long protocol demanded more human menopause gonadotropin (hMG) and sometimes causes unnecessary delay in the procedure. A new 7-day GnRHa/hMG protocol required to conserve cost and time is thus evaluated for better outcome. METHODS: Sixty consecutive IVF candidates less than 40 years of age were recruited for the study. Cases with severe male factor or polycystic ovarian disease were excluded. The perspective candidates were divided into two groups, one received the traditional, GnRHa2hMG protocol and the other received the new 7-day regimen. RESULTS: When comparing the results in pregnancy rate (33.3% vs 30%), cleavage rate (75.7% vs 75.5%), and the number of oocyte obtained (5.96 +/- 0.91 vs 6.63 +/- 0.90), the 7-day GnRHa/hMG protocol is as good as those of the traditional regimen. The amount of hMG used nevertheless was significantly less (21.48 +/- 0.78 vs 50.59 +/- 2.07). CONCLUSIONS: The new regimen will surely reduce the cost to relieve patient's financial burden and to increase patient's comfort.

Adult↗
PubMed1995

Changes in phases and crystallinity of plasma-sprayed hydroxyapatite coatings under heat treatment: a quantitative study.

With three kinds of plasma-sprayed hydroxyapatite coatings (HACs) prepared, the objectives of this study were (1) to establish the calibration methods for quantitatively measuring the concentration of impurity phases and the degree of crystallinity of the HACs, and (2) to explore the effects of postheat treatments at various temperatures in vacuo on the changes of phases and crystallinity of the HACs. By the internal standard method used, the concentrations of impurity phases, such as alpha-TCP, beta-TCP, and TP, of the assprayed HACs were significantly higher than those measured by the direct intensity-ratio method, and the CaO phase was lower than the direct intensity-ratio method. When the HACs were heat treated in the temperature interval 630-850 degrees C, the concentrations of impurity phases obviously decreased, and the coating crystallinity apparently increased. After annealing at 850 degrees C, an HAC consisting of at least 95% crystallinity with few impurity phases was obtained. As the annealing temperatures in the interval 850-1000 degrees C were applied, however, the HA phase seriously decomposed, resulting in the appearance of a large number (higher than 20 wt%) of impurity phases in the HACs. This work suggests that the optimum heat treatment conditions in vacuo for maximizing crystallinity and minimizing impurity phases of the HACs do not occur at the same temperature.

Alloys↗
PubMed1995

The antinociceptive effect of S-(+)-ibuprofen in rabbits: epidural versus intravenous administration.

This study was designed to determine whether systemic absorption plays any role in the antinociceptive effect of epidural (EP) sodium S(+)-ibuprofen (IB). One week after surgical implantation of EP catheters, six rabbits were given EP injections with either normal saline (NS) 0.4 mL or IB 10 mg in 0.4 mL NS (Group 1) on separate days. Each animal was injected with IB 10 mg intravenously (i.v.) on another day. Six control rabbits (Group 2) had neither surgery nor any injection. Analgesic testing was performed using electric stimulation through two electrocardiogram (ECG) skin electrodes with built-in adhesive, attached to shaved hip areas using 50 V, 1 Hz, 3 ms, before and 0.5,1,2 and 3 h after injection in Group 1, and in similar times in controls. The 95% confidence intervals (CI) of the mean difference between baseline and maximal nociceptive response latency of all groups were compared using analysis of covariance (ANCOVA) adjusted for baseline measurements. This comparison covered all possible pairs among all groups. Significant antinociceptive effects were seen after EP IB but not after control or i.v. IB. Neither motor dysfunction nor evidence of systemic toxicity or neurotoxicity was observed in any animal.

Analgesics↗
PubMed1995

Comparison of human menopausal gonadotropin and follicle-stimulating hormone with gonadotropin-releasing hormone agonist desensitization for controlled ovarian hyperstimulation in in vitro fertilization.

BACKGROUND: A pregnancy in patients treated with gonadotropin-releasing hormone agonists (GnRHa) using follicle-stimulating hormone (FSH) alone was first reported by Shaw et al. in 1991. Recently, several comparative trials have shown that FSH is as effective as human menopausal gonadotropin (hMG) in this indication. In other words, the residual endogenous levels of luteinizing hormone (LH) in GnRHa treated cycles may be generally sufficient to support FSH-induced follicular development to exempt from the co-administration of exogenous LH. METHODS: A total of 42 consecutive candidates for in vitro fertilization (IVF) participated in a prospective randomized study. In this study, the efficacy of two different gonadotropins (Pergonal and Metrodin, Serono, Italy) in inducing ovulation was investigated. All treated women were less than 40 years of age and had received a long desensitized protocol by a GnRHa (Leuprolide acetate, Takeda or Decapeptyl, Ferring). Ovarian inactivity was monitored by plasma estradiol and LH concentration. After the pituitary gland was down-regulated, all patients were given either hMG (n = 25) or FSH (n = 17) for controlled ovarian hyperstimulation (COH). RESULTS: The mean number of gonadotropin ampoules and the peak estradiol level were significantly higher in hMG group than in the FSH group. No significant differences were found between both groups in the incidence of cancelled cycles, failed oocyte recovery, mean number of oocytes recovered per patient, the fertilization and embryo cleavage-rate. However, the hMG group demonstrated a higher pregnancy and abortion rate. CONCLUSIONS: There is no significant difference between hMG and FSH stimulation when used following GnRHa desensitization for COH, so the cost should be considered.

Adult↗
PubMed1994

The thumb's knuckle. Flexibility in the thumb subdomain of T7 RNA polymerase is revealed by the structure of a chimeric T7/T3 RNA polymerase.

We have solved the structure of a chimeric T7/T3 RNA polymerase (RNAP) in an orthorhombic crystal by molecular replacement with the T7 RNAP structure determined from a monoclinic crystal. The structure of the protruding "thumb" subdomain of the polymerase appears very different in these two crystals apparently because of differences in packing contacts made by the thumb subdomain. These observations support the proposal that the thumb subdomain is flexible and can wrap around bound template to obstruct polymerase: template dissociation during processive synthesis.

Amino Acid Sequence↗
PubMed1994

Crystals of glutamine-binding protein in various conformational states.

Crystals of glutamine-binding protein (GlnBP) in various conformational states have been obtained. Crystals of the ligand-free "open" state (denoted form B) have unit cell dimensions a = 86.3 A, b = 86.3 A, c = 81.5 A, alpha = beta = gamma = 90 degrees and diffract to about 2.3 A resolution. An analysis of the intensity data using an Requiv plot indicates that the crystal system is orthorhombic, space group P2(1)2(1)2(1). Crystals of the ligand-bound "open" state (form B*) are obtained by soaking form B crystals with glutamine (Gln) and diffract to about 1.9 A. Crystals of the GlnBP-Gln complex in a ligand-bound "closed" state (form C) belong to space group P2(1)2(1)2(1) with a = 62.0 A, b = 65.7 A and c = 121.8 A and diffract to about 2.3 A. Crystals of a selenomethionyl GlnBP (form B') are isomorphous to form B crystals and diffract to about 2.1 A resolution.

Carrier Proteins↗
PubMed1994

The octameric histone core of the nucleosome. Structural issues resolved.

The crystal structure of the histone octamer has now been determined at 3.1 A resolution and refined to a crystallographic R value of 25.5%. The overall shape of the structure is significantly different from that originally reported by Burlingame et al. and its length is now in agreement with that observed by Klug et al. in their low-resolution studies. The experimental intensity data used in constructing the new electron density map were the same as those used by Burlingame et al. for the original electron density map. In addition, the methods used in producing the new density map were also the same as those for the original map. The only difference between the two calculations was the selection of the heavy-atom location. The large change seen in the structural image (110 A x 70 A x 70 A versus 55 A x 70 A x 70 A) was due to a relatively small change (2.27 A shift) of the heavy-atom site. The fact that the shape and size of the original structure were incorrect is surprising and unusual, since the electron density map that produced the original model was clear for most parts of the structure; one could easily see the well-formed right-handed helices of the H2A and H2B molecules, and the ordered parts of the H2A and H2B molecules could be easily traced from end to end. A comparison of the two maps shows that the original image was derived from two fused copies of the correct structure rotated by +/- 120 degrees from its true location along a rotation axis parallel to the z-axis and the image seen was a partial (about 19.5%) overlap of two molecules. An explanation is given as to how such a small shift of the heavy-atom position could create such a double image in the unit cell, and how the original electron density map could be converted to the new map by a phase modification in the Fourier synthesis. This study resolves the differences between the analyses of the shape and size of the histone octamer structure.

Crystallography, X-Ray↗
PubMed1994

A surface mutant (G82R) of a human alpha-glutathione S-transferase shows decreased thermal stability and a new mode of molecular association in the crystal.

A chimeric enzyme (GST121) of the human alpha-glutathione S-transferases GST1-1 and GST2-2, which has improved catalytic efficiency and thermostability from its wild-type parent proteins, has been crystallized in a space group that is isomorphous with that reported for crystals of GST1-1. However, a single-site (G82R) mutant of GST121, which exhibits a significant reduction both in vitro and in vivo in protein thermostability, forms crystals that are not isomorphous with GST1-1. The mutant protein crystallizes in space group P2(1)2(1)2(1), with cell dimensions a = 49.5, b = 92.9, c = 115.9 A, and one dimer per asymmetric unit. Preliminary crystallographic results show that a mutation of the surface residue Gly 82 from a neutral to a charged residue causes new salt bridges to be formed among the GST dimers, suggesting that the G82R mutant might aggregate more readily than does GST121 in solution, resulting in a change of its solution properties.

Amino Acid Sequence↗